This invention relates to cyclones and, more particularly, to an improvement in a cyclone, with which the pressure loss is reduced and the exhaust gas from the cyclone has a reduced residual dust concentration so that dust separation efficiency can be increased.
The vertical cyclone utilizes centrifugal force to separate and capture dust in gas, and it is extensively used for cement firing equipment and the like.
An example of the cyclone of this type is disclosed in Japanese Utility Model Application Laid-open No. 56-121453. In the disclosed cyclone, a cylindrical shell has a projecting peripheral wall portion inwardly projecting into the cyclone and terminating in the neighborhood of the joint of an inner portion of a gas supply duct and the cylindrical drum. The inwardly projecting peripheral wall portion has an effect of reducing the proportion of the whirling flow in the cyclone that strikes and joins a dust-containing gas stream introduced from the gas supply duct, thus reducing the pressure loss.
Even with this construction, however, dust particles of comparatively small diameters that have not been separated and brought to the periphery of the cylindrical shell reach and strike the inwardly projecting vertical wall portion thereof to disturb the status of flow of dust, so that part of the dust is introduced into and carried along by the exhaust gas being exhausted through a gas exhaust duct, thus lowering the dust separation efficiency of the cyclone. This shortcoming imposes restrictions on the extent to which the projecting wall portion projects into the cylinder, so that the effect of pressure loss reduction has been insufficient.
In addition, the gas exhaust duct is provided concentrically with the cylindrical shell, so that the space defined between the cylindrical shell and gas exhaust duct has a substantially constant cross-sectional area in the axial direction. Therefore, gas whirls in the space at a substantially constant speed, and no substantial axial velocity component is given. The stream of gas and dust thus whirls along the space a large number of revolutions, leading to high frictional resistance between downward and upward whirling gas streams and consequent high pressure loss. Besides, many revolutions lead to a long retention time of dust in the cyclone, thus increasing the quantity of residual dust in the cyclone to increase the quantity of dust carried along by the exhaust gas and to lower the dust separation efficiency of the cyclone.